1. He’s too nice
In an election year where the Democratic base fell in love with the pugnacious styles Sanders and Warren, Kaine’s low-key, nice-guy persona feels like a bit of a letdown. Clinton is picking a Democrat that Republicans like, which in this polarized climate feels like a betrayal. He’s the type of lawmaker who seeks to build bipartisan consensus, not the kind who hold the line on the liberal position. Arizona Republican Sen. Jeff Flake — who’s refused to endorse Trump — even had good words to say about Kaine after the news broke.
2. He’s too white
A Southern, white Republican is not exactly the future of the party. Not picking a woman or a minority also feels like a disappointment among base voters. Especially if they feel like women (Warren) and Latinos (Labor Secretary Tom Perez) were passed over for the white guy.
3. He’s too moderate
Except, Kaine isn’t really. He has a zero percent rating from the American Conservative Union. But his bipartisan style often lends itself to a perception that he’s a moderate. On some issues, he definitely strikes a more centrist tone.